1. Field of the Invention
This invention relates generally to compact and ultra-wideband antennas and, more particularly, to coupled sectorial loop antennas (CSLA) for ultra-wideband applications.
2. Discussion of the Related Art
Various applications for ultra-wideband (UWB) wireless systems are known in the art, including ground penetrating radar, high data rate short range wireless local area networks, communication systems for military applications, UWB short pulse radars for automotive and robotics applications, etc. UWB wireless systems require antennas that are able to operate across a very large bandwidth with consistent polarization and radiation pattern parameters over the entire band. Various techniques are known in the art to design antennas with wideband impedance matched characteristics.
Traveling wave antennas and antennas with topologies that are invariant by rotation are inherently wideband and have been extensively used in the art. Self-complimentary antenna concept provides a constant input impedance irrespective of frequency, provided that the size of the ground plane for the slot segment of the antenna is large and an appropriate self-complimentary feed can be designed. Theoretically, the input impedance of self-complimentary antennas is 186 ohms, and thus, these antennas cannot be directly matched to standard transmission lines having a 50 ohm impedance. Another drawback of self-complimentary antenna structures is that they cannot be printed on a dielectric substrate because the dielectric constant of the substrate perturbs the self-complimentary condition.
Another technique for designing wideband antennas is to use multi-resonant radiation structures. Log-periodic antennas, microstrip patches with parasitic elements, and slotted microstrip antennas for broadband and dual-band applications are examples of such multi-resonant radiating structures.
The electric dipole and monopole above a ground plane are perhaps the most basic types of antennas. Variations of these antennas have recently been introduced for obtaining considerably larger bandwidths than the traditional dipole and monopole antenna designs. Impedance bandwidth characteristics of circular and elliptical monopole plate antennas are also known in the art. Wideband characteristics of rectangular and square monopole antennas are also known, and a dielectric loaded wideband monopole has been investigated in the art. One drawback of these types of antennas is that the antenna polarization as a function of frequency changes.